Method of manufactubing resistance



Patented Apr. 26, 1949 METHOD OF MANUFACTURING RESISTANCE ELEMENTS Adriaan Abraham Padmos and Evert Johannes Willem Verwey, Eindhoven, Netherlands, assignors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee No Drawing. Application May 3, 1946, Serial No. 667,106. In the Netherlands April 29, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires April 29, 1962 4 Claims. (01. 25157) In a copending application for a U. S. Patent Serial No. 668,471, flied May 9, 1946, a method is disclosed with the aid of which it is possible to manufacture sintered resistance bodies which have a high resistance value and a low temperature coeflicient of the resistance and which consist of an insulatin mass of magnesia in which particles of reduced electrically conducting titanium oxide are dispersed in a quantity of 3% at the most.

According to this method, a mixture of magnesia and titanium oxide is sintered at a temperature beyond 1700 0., preferably of from 1800 to 2000 C., in a reducing gas stream whose content of oxygen with respect to the hydrogen present therein amounts to at least 0.003% by volume and for the rest is exactly adjusted in connection with the desired resistance value.

For Wholesale manufacture this method can b further improved in various respects.

In the method described in the copending application, the content of oxygen of the reducing gases which surround the resistance bodies during the sinterin operation is particularly important in connection with the obtainment of the desired resistance value. Now it has been found that this content of oxygen can be regulated not only by the choice of the composition of the gas introduced but also by adjusting the speed of flow. The correct speed of flow may be ascerreduction may have an appreciable influence on the reducing character thereof. I

For carrying the invention into efiect use may be made with particular advantage of the embodiment described in the copendin application wherein the starting point is formed by partly reduced titanium oxide or by corresponding mixtures of titanium dioxide and titanium because in this case a smaller amount of oxygen is set free and consequently the content of oxygen of the gas surrounding the resistance bodies can be regulated more easily by means of the speed of flow. Now it has been found that such a favourable influence is exerted not only by titanium in the starting mixture but also by silicon and carbon. Moreover, these additions bring about a slight displacement of the temperature coefficient of the resistance in the positive direction, which is desirable for some applications.

' are retained.

The invention will hereinafter be explained more fully with reference to one example.'

Magnesia which has been preliminarily heated to 1300-1400 (7., is ground, jointly with approximately 4% by weight of rutile and 1% by weight of carbon with alcohol, during 8 hours in a ballmillwhereupon, with the use of nitrocellulose as a binder, the material is pressed into rods which are dried. Subsequently, these rods are sintered durin about 6 minutes in a gas stream consisting of a mixture of about 90% by volume of nitrogen and 10% by volume of hydrogen, this gas being purified by causing it to pass over finely divided Cu present on infusorial earth and heated to 300 C. and dried with the aid of solid KOH, liquid oxygen and P205. The heating takes place with the aid of a molybdenum tube heated by an electric current to 1800-1900 C., said tube having a length of 30 cms. and an internal diameter of 8 mms. If the speed of the flowing gas is adjusted to 16 litres per minute we obtain resistances which, when having a length of 18 mms. and a diameter of 1.35 mms., have at room temperature a resistance value of about 1.5x10 ohms. At a temperature of 300 C. the resistance value is approximately of the value at room temperature.

What we claim is:

1. A method of manufacturing resistanceelemerits, comprising the steps of sintering a mixture of magnesium and titanium oxides at a temperature greater than about 1700" C. in a reducing gas stream containing hydrogen and oxygen in the amount of at least 0.003% by volume of the hydrogen, and controlling the amount of oxygen in said reducing gas stream by adjusting the flow of said reducing gas over said sintered mixture.

2. A method of manufacturing resistance elements comprising the steps of sintering a mix- 1 's of magnesium and titanium oxides containing small addition of an element selected from the group carbon and silicon at a temperature greater than bout 1700"C.-' in :a reducing gas stream containin hydrogen and-oxygen in the amount of at least 0.003% by volume of the hydrogen, and controlling the amount of oxygen in said gas stream by adjusting. the flow of said reducing gas over said sintered mixture.

3. A method of manufacturing resistance elements, comprising the'steps oi sintering a mixture containing magnesium oxide, approximately 4% by weight of titanium oxide, and a small addition of an element selected from the group carbon and silicon at a temperature greater than about 1700 C. in a reducing gas stream containing hydrogen and oxygen in the amount of at least 0.003% by volume of the hydrogen, and controlling the amount of oxygen in said reducing gas stream by adjustin the flow of said reducing gas over said sintered mixture.

4. A method of manufacturing resistance elements, comprising the steps of sintering a mix- Number Name Date 1,992,482 Heuer Feb. 26, 1935 20 2,021,520 Reichmann NOV. 19; 1935 2,095,982 Heany Oct. 19, 1937 2,316,228

REFERENCES CIT The following references are of record in the file of this patent:

UNITED STATES PATENTS Erdmann Apr. 13, 1943 

